The ever-increasing demand for battery-powered electronic equipment has driven the need for improved rechargeable electrochemical cells having high specific energies. The most attractive of these types of cells are the lithium-ion cells, Lithium-ion cells and batteries are secondary (i.e., rechargeable) energy storage devices well known in the art. The lithium-ion cell, known also as a rocking chair type lithium battery, typically comprises a carbonaceous negative electrode that is capable of intercalating lithium-ions, a lithium-retentive positive electrode that is also capable of intercalating lithium-ions, and a separator impregnated with non-aqueous, lithium-ion-conducting electrolyte therebetween. The electrolyte in such lithium-ion cells comprises a lithium salt dissolved in a non-aqueous solvent which may be (1) completely liquid, (2) an immobilized liquid, (e.g., gelled or entrapped in a polymer matrix), or (3) a pure polymer. The electrolyte is incorporated into the pores of the positive and negative electrode and in a separator layer between the positive and negative electrode.
Lithium-ion cells are often made by laminating thin films of the negative electrode, positive electrode and separator together wherein the separator layer is sandwiched between the negative electrode and positive electrode layers to form an individual cell. Conventional cells have typically been enclosed in a rigid case, typically made of stainless steel, to apply pressure to the cell components to maintain good electrical connections between the components. However, the trend is to reduce the size and weight of battery cells by replacing the rigid case with a polymer-metal laminate packaging material. The laminate packaging typically comprises a metal sheet, such as an aluminum foil, between two polymer films. One problem experienced with these laminate packaging materials is delamination of the polymer from the aluminum foil when exposed to the battery electrolyte, and subsequent corrosion of the aluminum by the corrosive electrolyte. Another problem encountered with the laminate packaging materials is a poor seal at the interface between the packaging material and the conductive leads. U.S. Patent Application Publication No. 2003/0031926 A1 provides a surface treatment for the conductive leads to provide a more reliable hermetic seal between the conductive leads and the packaging material. However, there exists a need for an improved packaging material that addresses the problem of delamination of the polymer from the metal sheet and the resulting corrosion.